1. Field of the Invention
The present invention relates generally to gear trains of multi-step transmissions installed in vehicles and, more particularly, to the structure of a gear train of a multi-step transmission which can shift gears among nine forward speeds and one reverse speed.
2. Description of Related Art
Generally, conventional nine or more speed transmissions for vehicles include four or more sets of planetary gears to embody a plurality of gear shift ratios.
However, use of many sets of planetary gears increases the volume or length of a transmission, thus making it difficult to install the transmission in a vehicle. Further, a set of planetary gears typically has reduced power transmission efficiency, compared to that of a simple external gear train or a simple internal gear train. In other words, the planetary gears are disadvantageous from the point of view of the power transmission efficiency.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.